1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer to a flat mirror finish, and more particularly to a polishing apparatus having an exhaust device for exhausting air in the polishing apparatus.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnection is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 .mu.m wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening thesurfaces of semiconductor wafers is to polish them with a polishing apparatus, and such a process is called Chemical Mechanical polishing.
Conventionally, a polishing apparatus has a polishing section comprising a turntable and a top ring which rotate at respective individual speeds. A polishing cloth is attached to the upper surface of the turntable. A semiconductor wafer to be polished is placed on the polishing cloth and clamped between the top ring and the turntable. An abrasive liquid containing abrasive grains is supplied onto the polishing cloth and retained on the polishing cloth.
During operation, the top ring exerts a certain pressure on the turntable, and the surface of the semiconductor wafer held against the polishing cloth is therefore polished to a flat mirror finish while the top ring and the turntable are rotated.
The polishing apparatus also has a cleaning section for conveying the semiconductor wafers and cleaning the semiconductor wafers. The cleaning section comprises a workpiece conveying robot for taking a semiconductor wafer out of a cassette and delivering the semiconductor wafer to the polishing section, a cleaning device for cleaning the semiconductor wafer which has been polished, a drying device for drying the semiconductor wafer which has been cleaned, and the like. The workpiece conveying robot, the cleaning device, the drying device and the like are housed in a single chamber.
FIG. 6 shows one conventional cleaning section of the polishing apparatus. As shown in FIG. 6, the cleaning section 150 comprises a base 151 comprising a plurality of structural members 157 such as H sections, a workpiece conveying robot 153 mounted on the central portion of the base 151, and a cleaning device 155 mounted on the base 151 and arranged on one side of the workpiece conveying robot 153. A drying device (not shown) is also mounted on the base 151. The structural members 157 are arranged not only at peripheral portions of the base 151 but also at the installation locations of various devices for supporting their weight.
An exhaust duct 159 is provided in the interior of the base 151. The exhaust duct 159 has a number of intake openings 161, and an upper end which is connected to a main exhaust duct 163 extending vertically through the base 151. The main exhaust duct 163 has an upper end which is connected to a filter unit 165. When a fan (not shown) provided in the filter unit 165 is driven, air in the cleaning section 150 moves downwardly, flows in the exhaust duct 159 through the intake openings 161, and then flows in the filter unit 165 through the exhaust duct 159 and the main exhaust duct 163. Dust or particles in the air are removed by the filter unit 165, and clean air is supplied into the interior of the cleaning section 150 from the filter unit 165. Thus, air in the cleaning section 150 is always kept clean.
However, in the conventional apparatus, since the exhaust duct 159 dedicated to exhaust of the cleaning section 150 is provided in the interior of the base 151, a large space for the exhaust duct 159 is required in the base 151. The base 151 bulky. Further, the base 151 and the exhaust duct 159 are required to be manufactured individually and to be assembled separately to thus increase their manufacturing and assembling costs.